Of course, they struggle on the lows, so I'd like to build a subwoofer for them. My questions are:
-What should be cut off frequency?
-What should be the order of both of the crossovers?
-What should be the nominal power and sensitivity compared to the drivers - subwoofer to satellite ratio?
-Because of availability, I'd like to use a visaton speaker. Can you recommend me one?

The crossover of the sub could be made active with a variable cut off frequency, in case I get a bad frequency response.

Of course, they struggle on the lows, so I'd like to build a subwoofer for them. My questions are:
-What should be cut off frequency?
-What should be the order of both of the crossovers?
-What should be the nominal power and sensitivity compared to the drivers - subwoofer to satellite ratio?
-Because of availability, I'd like to use a visaton speaker. Can you recommend me one?

The crossover of the sub could be made active with a variable cut off frequency, in case I get a bad frequency response.

Hi,

Why not build a low footprint sub using the 8” Visaton AL 200 driver using a ported design.

IMO, best SQ if converting the most promising box(70L BR) recommended by the manufacturer to a T-TQWP.

My suggestions are: XO somewhere between 120-145 Hz using a 24 dB LP filter for the sub and for the FR 10 use a 12dB HP filter.

When placing the sub somewhere at 1 - 0.5Pi space angle: One Visaton AL 200 driver in a T-QWP will match the two FR 10:s sensitivity well.

PS: The driver offset distance is not correctly predicted in HR as the crude picture is depicting but this discrepancy is IME of minor importance...obvious noticed if simulated in MJK:s program using appropriate amount of damping material.